This invention relates to the major iron regulated protein (MIRP) of Neisseria gonorrhoeae, in isolated immunospecific antigenically, substantially pure form, and its use as a vaccine.
The membrane proteins expressed by N. gonorrhoeae when grown under iron-limitation have been examined. Norquist et al, FEMS Microbiol. Letters 4:71-75 (1978), described the presence of several high-molecular-weight (70,000 to 100,000) membrane iron-regulated proteins. Subsequent studies have confirmed the presence of these high-molecular-weight iron-regulated proteins Mietzner et al, Infect. Immun. 45:410-416 (1984); West and Sparling, ibid, 47:388-94 (1985), as well as a previously unidentified iron-regulated protein with an apparent molecular weight of ca. 37,000. Although no attempt was made to isolate the protein in pure form, sodium dodecylsulfate-polyacrylamide gel electrophoresis visualized with a sensitive silver stain indicated that this protein represented a major component of Sarkosyl-insoluble membrane preparations from gonococci grown under iron-limited conditions. For this reason, this protein is referred to as the major iron-regulated protein (MIRP). Mietzner et al, supra. All gonococci examined to date express this protein under conditions of iron-limitation and peptide maps indicate that the structure of this protein is highly conserved among two unrelated gonococcal strains. West et al, ibid, 47:388-394 (1985), examined the expression of the gonococcal iron-regulated proteins and determined that they were not coordinately regulated. In the presence of various iron-containing proteins as iron-sources, different gonococcal strains expressed different combinations of iron-regulated proteins. The MIRP was expressed in the presence of all of the iron-containing molecules tested. Although the consistant expression of this protein under all conditions of iron-limitation and its conservation among gonococci prompted speculation that this protein might play a central role in iron-acquisition by the gonococcus, to date note direct function in iron-uptake has been ascribed to the MIRP.
Heretofore, no successful vaccine has been available having efficacy against the numerous strains of N.g. One of the principal problems which has impeded the production of a vaccine is the antigenic heterogeneity of the N.g. microorganisms.
A reported solution to this problem of antigenic heterogenicity is the use of the common peptide region from gonococcal pilin. Such a peptide region is not found in MIRP. Therefore, it was surprising to discover that the MIRP from the various species of the genus Neisseria nevertheless are antigenically homogeneous.
To facilitate an understanding of the MIRP of N. gonorrhoeae, a method was developed to purify this protein in reasonable quantities. This permitted the discovery of the ability of the purified MIRP to stimulate the production of monoclonal antibodies to gonococcal microorganisms and its utility as a vaccine to protect against gonococcal infections in susceptible hosts.